No description available.

Thesis (Ph.D.)--Oregon, Dept. of Biology Vita Bibliography: l. 85-90

The research presented in this thesis covers two critical problems regarding lined pipes: dynamic impact and welding. A lined pipe consists of an inner layer (the liner) made of corrosion resistant alloy (CRA), e.g. AISI304 stainless steel, and an outer layer made of low carbon steel, e.g. carbon-manganese steel, C-Mn. To manufacture the lined pipe, a special heat treatment, known as tight fit pipe (TFP), based on cooling the liner to -200°C, heating the backing pipe to +500°C and inserting the liner inside the outer pipe, was used in this work. Both welding and impact with external objects are responsible for accumulating high levels of plastic strains and residual stresses which could lead to failure in the pipe sometime after the impact or the welding. The special welding process used in lined pipes typically consists of the overlay welding (inner welding) of the liner with the C-Mn steel pipe for each segment and the girth welding (outer welding) of the two segments. To simulate this welding process using the ABAQUS code, nonlinear heat-transfer and mechanical finite-element (FE) analyses have been conducted. A distributed power density of the moving welding torch and a non-linear heat transfer coefficient accounting for both radiation and convection have been used in the analysis and implemented in ABAQUS user-subroutines. The modelling procedure has been validated first against previously published experimental results for stainless steel and carbon steel pipe welding separately. The model has been then used to determine the isotherms induced by the one-pass weld overlay and the one-pass girth welding and to clarify their influence on the transient temperature field and residual stress in the lined pipe. Furthermore, the influence of the cooling time between weld overlay and girth welding and of the welding speed have been examined thermally and mechanically as they are key factors that can affect the quality of lined pipe welding. The same FE numerical procedure to analyse line pipe welding is then applied to simulate six cases experimentally tested in the lab within this project. Furthermore, two cases have been analysed first, namely a reference case, in which the effect of the TFP pre-heat treatment is neglected, and a second one where the pre-heat treatment has been taken into consideration. During welding, the FE thermal history and mechanical strain results for both cases correlate well with the experimental ones in the region with the highest residual stresses, because the effect of initial residual stresses is cancelled in the regions subject to very high temperatures. After welding, the numerical and experimental results have proved that the initial residual stresses due to the TFP pre-heat treatment are reasonably important in the liner whereas they are practically negligible in the C-Mn pipe. The same reference case is then compared numerically and experimentally with further five parametric cases to study the effect of welding properties (weld overlay and girth welding materials), geometric parameters (using weld overlay and liner) and welding process parameters (heat input). The numerical temperature fields and residual stresses are in good agreement with their experimental counterparts for all cases. The dynamic impact problem is a crucial one for lined pipes because of the reduction in the thickness of the outer pipe ensured by the internal protection from corrosion given by a thinner liner. In this case, the lined pipe is more affected by potential impact with external objects (so-called 'third party interference' in the Oil and Gas industry). In general, a dent produced by a freely dropped weight is responsible to a large extent of catastrophic failure in pipelines. Therefore, in this work, 3D FE models have been developed to simulate the mechanism of vertical free drop of a weight from different heights resulting in damage in the pipe. Models have been executed using a three-dimensional non-linear explicit-dynamics FE code, ABAQUS/EXPLICIT. In order to precisely simulate the response of the pipe to subsequent impacts and spring back, an elastic-plastic constitutive law is adopted using the isotropic Hooke's law and a Von Mises yield criterion, with work hardening based on an isotropic hardening rule associated with the equivalent plastic strain rate. Strain-rate dependent properties are specified for both materials, C-Mn and AISI304, to take into account the change in velocities during impact. The numerical strain results are reasonably consistent with the experimental ones recorded by four strain gauge rosettes positioned symmetrically around the dent centre. Numerical and experimental results are comprehensively analysed and discussed also in terms of practical implications in the industry.

Portland cement (PC) concrete has historically been the most commonly used construction material within the United Arab Emirates (UAE), however, as the demand increases to reduce CO2 emissions most of newly-built facilities make use of modern concrete formulations adopting various PC substitutes, and these ‘blended cements’ typically involve mineral admixtures such as ground granulated blast-furnace slag (GGBS), fly ash (FA) and silica fume (SF). The percentage of PC replaced in these concrete mixtures varies depending on the type of cement and design criteria as well as other related issues such as fire resistance. The use of PC replacements in ready-mixed concrete has been made obligatory in Dubai from 1st April 2015. This recent move towards using greener concretes has been implemented with little research on their heat resistant properties and as such an understanding of their behaviour on exposure to high temperatures in structural fires is limited. Furthermore, the applicability of forensic engineering techniques for the assessment of any deterioration in these concrete formulations is largely untested. For this reason, a range of analytical techniques have been investigated as part of this research in order to establish the chemical and physical changes taking place as well as the practical applicability of the techniques used. Three key areas were addressed as part of this research. Firstly, a review of urban fires in Dubai and a survey of fire investigation related issues within the region was undertaken. This formed a base from which the research questions could be refined. Secondly, nine concrete mixtures were assessed using 15 analytical techniques. The concrete mixtures were exposed to 4 temperatures (150°C, 300°C, 600°C, and 900°C) within a muffle furnace and the chemical, mineralogical, physical and mechanical changes were investigated using TGA, DSC, FTIR, XRD, SEM, EDX, BET surface area, residual compressive strength, density loss, carbonation depth, visual colour change, rebound hammer, UPV, portable 3D laser scanning and micro CT scanning. Finally, a set of test concrete mixtures most closely linked to those used in construction in the UAE were exposed to a real fire and were analysed post fire using a reduced set of the analytical techniques. The techniques were assessed as to how well they could define the temperature range to which the concrete had been exposed as well as ascertaining the degree of concrete degradation based on the confirmation of the chemical, mineralogical, physical and mechanical changes which had occurred. Findings indicate that the use of blended cement concrete improves the thermal resistance of the material when compared with PC concrete up to a certain temperature, usually below 600°C. Discolouration in heated concrete sections were visualised using simple digital photography. Changing the cement composition influenced the rate of carbon ingress into the concrete matrix, however this did not result in any significant colour change in heated mortar surfaces. By contrast, colour changes within the aggregates was observed at temperatures > 300°C and was strongly determined by the mineralogy of the material. The analytical data demonstrated that there were three temperature regions that provide measurable data and information to inform fire investigators of the thermal history experienced by the concrete matrix. Between 70°C-200°C the evaporation of non-chemically bound water and dissociation of ettringite, gypsum and gel-like calcium silicate hydrate (CSH) occur, and can be detected using a range of the techniques used. The heat flux required for these reactions to occur was greater in all mixtures containing GGBS. Observed chemical and physical transformations between 300°C and 500°C were mainly due to the oxidation of iron hydroxide and the dehydroxylation of portlandite. Further chemical changes at 650°C and above were identified as a direct result of the decarbonation of CaCO3. At elevated temperatures, the absence of certain minerals within the concrete formulations provided an indication of the temperature which would have been reached by the concrete matrix. It was also revealed that in some cases the minerals present rehydrated during cooling of the concrete and this was also detectable using a number of the analytical methods employed. For the test samples exposed to real fire conditions, the rebound hammer, UPV and compressive strength measurements all provided good indications of physical losses experienced by the concrete, however these methods were not good estimators of the exposure temperature. The results from TGA, DSC and FTIR in particular were more reliable but differed from the reference models in that water used in suppression and absorbed by the concrete affected some of the predicted features. XRD also revealed peaks which could be related to various phases of change within the concrete, which was helpful in revealing the thermal history of concrete. Discolouration of cross-sections of the concrete samples produced trends similar to the lab-heated specimens however this was hard to visualise on the surface of the concrete due to the soot layer resulting from the fire. The results characterised, for the first time, chemical and physical changes occurring within a range of concrete mixtures used in the UAE and linked these to specific temperature ranges to which the concrete were exposed. Furthermore, this work has demonstrated that a number of the analytical techniques used can be helpful in the determination of the thermal history of concrete which has been exposed to fire conditions.

Yes / The possibility of using differential pre‐heating prior to supramolecular gelation to control the balance between hydrogen‐bonding and aromatic stacking interactions in supramolecular gels and obtain consequent systematic regulation of structure and properties is demonstrated. Using a model aromatic peptide amphiphile, Fmoc‐tyrosyl‐leucine (Fmoc‐YL) and a combination of fluorescence, infrared, circular dichroism and NMR spectroscopy, it is shown that the balance of these interactions can be adjusted by temporary exposure to elevated temperatures in the range 313–365 K, followed by supramolecular locking in the gel state by cooling to room temperature. Distinct regimes can be identified regarding the balance between H‐bonding and aromatic stacking interactions, with a transition point at 333 K. Consequently, gels can be obtained with customizable properties, including supramolecular chirality and gel stiffness. The differential supramolecular structures also result in changes in proteolytic stability, highlighting the possibility of obtaining a range of supramolecular architectures from a single molecular structure by simply controlling the pre‐assembly temperature. / FP7 Ideas: European Research Council. Grant Number: 258775

Les fibres optiques sont présentes de manière incontournable dans les télécommunications et les réseaux d’accès à internet. Longs fils de verre fabriqués en silice vitreuse ultra pure, elles permettent de transmettre des informations sur de longues distances sous forme de signaux lumineux. Malgré leurs capacités de transmission déjà excellentes, la réduction des pertes optiques demeure un enjeu économique. En effet, en dessous d’une certaine atténuation, il est possible de supprimer des amplificateurs localisés dans des zones peu accessibles où leur installation est très couteuse. L’objectif de ce travail de thèse est donc d’explorer de nouvelles voies permettant de réduire significativement l’atténuation du signal optique.La silice est un élément de choix pour les applications optiques du fait de ses propriétés physico-chimiques (haute transparence de l’IR à l’UV, forte résistance mécanique,…). L’incorporation de composés dans le verre de silice modifie ses caractéristiques (viscosité, densité,…) sans détérioration des propriétés optiques ; en particulier l’ajout de fluor F diminue son indice de réfraction tandis que l’oxyde de germanium GeO2 l’augmente. En revanche, le désordre structural du verre augmente avec ces ajouts et, par conséquent, l’atténuation de même. Ce désordre dépend de l’histoire thermique et est décrit au moyen de la température fictive Tf qui correspond à la température pour laquelle la structure du verre a été gelée. La Tf du verre détermine de nombreuses propriétés du matériau telles que les fluctuations d’indice de réfraction et de densité.La diffusion Rayleigh est la principale source de pertes dans les fibres optiques, représentant une part de ~90% à la longueur d’onde de 1550 nm. Cette diffusion trouve son origine dans les fluctuations de constante diélectrique dont deux types de contributions sont déjà connues : les fluctuations de densité et les fluctuations de concentration. En appliquant une approche thermodynamique, un autre terme est proposé pour compléter cette description : les fluctuations de température fictive, résultant d’une distribution des temps de relaxation du verre. Cette approche a mis en évidence l’importance d’étudier la relation existante entre la densité ρ et la Tf d’une part, et entre l’indice n et la Tf d’autre part, afin de réduire les pertes par diffusion Rayleigh.Dans une fibre optique, ce sont les conditions de fibrage essentiellement, c’est-à-dire la température, la tension et la vitesse, qui déterminent le passé thermique du matériau. Une étude expérimentale a permis de distinguer l’impact de ces conditions sur les pertes par diffusion dans des fibres monomodes conventionnelles. Les connaissances sur l’origine des objets diffusants (tailles et formes) dans les fibres d’histoires thermiques différentes ont pu être approfondies. Idéalement, il faudrait pouvoir s’affranchir des conditions de fibrage. Contrairement aux autres verres d’oxydes, le verre de silice admet un comportement dit ‘anormal’ pour sa densité : celle-ci augmente avec la température fictive. Cette anomalie disparait en incorporant une certaine quantité d’éléments chimiques (F, Cl, GeO2 mais pas TiO2) dans le matériau. Nous avons montré que certaines compositions, en supprimant la sensibilité de la diffusion Rayleigh à la Tf, permettent de minimiser les pertes optiques de la famille de fibres que nous avons étudiées.La spectroscopie Raman a ensuite été utilisée afin de comprendre l’origine structurale de cette anomalie. Les mesures réalisées ont montrées que les bandes D1 et D2 reliées à la vibration des petits cycles de tétraèdres dans le verre ne sont pas corrélées à la densité macroscopique. En conséquence, elles ne constituent pas une signature fiable du phénomène de densification dans les verres binaires. Des études complémentaires sur la coordinence du silicium dans la matrice sont nécessaires pour pouvoir conclure sur l’origine structurale de l’anomalie de la silice. / Optical fibers are inevitably present in telecommunications and Internet access networks. Long glass threads made of ultra-pure vitreous silica, they allow to relay information on long distances in the form of light signal. Despite their good transmission capacities, the reduction of optical losses remains an economical stake. Indeed, under a certain attenuation, it is possible to avoid amplifiers located in hardly accessible area where their setting is very expensive. The objective of this work is thus to explore new ways allowing to reduce significantly optical signal attenuation.The silica is a specific element for optical applications because of its physical chemistry properties (high transparency from IR to UV, strong mechanical resistance,…). Adding components in silica glass changes its characteristics (viscosity, density,…) without strong deterioration of optical properties. Especially, the addition of fluorine decreases the refractive index whereas germanium oxide GeO2 increases it. However, the glass structural disorder increases, and, therefore the optical attenuation as well. The disorder depends on thermal history. It is described by means of fictive temperature Tf that corresponds to the temperature at which the glass structure is frozen. The Tf of glass determines many material properties such as the fluctuations of refractive index and density. Rayleigh scattering is the main reason of optical losses in optical fibers, representing ~90% at 1550 nm wavelength. This scattering originates from the dielectric constant fluctuations, which contain two kinds of contributions: the density and the concentration fluctuations. By applying a thermodynamics approach, another term is suggested to complete this description: the fictive temperature fluctuations, resulting from a distribution of glass relaxation times. This approach highlighted importance of studying the relationship between density ρ and Tf on one hand, and between index n and Tf on the other hand, in order to reduce the Rayleigh scattering losses.In optical fiber process, Tf is essentially defined by the drawing conditions, i.e. furnace temperature, fiber drawing tension and speed. An experimental study allowed distinguishing the impact of these conditions on scattering losses in single mode conventional fibers. The knowledge about the origin of scattered objects (sizes and shapes) in fibers with different thermal histories has been made deeper. Ideally, it should be better to be disconnected from the drawing conditions.Contrary to the other oxide glasses, silica glass presents an anomalous behavior for its density: this one increases with fictive temperature. This anomaly disappears by adding a certain amount of chemical elements (F, Cl, GeO2, but not TiO2) in the material. We showed that some compositions, by deleting sensitivity of Rayleigh scattering to Tf, allows minimizing optical losses in the fibers family we studied. Raman spectroscopy has been then used in order to understand structural origin of this anomaly. Measurements revealed that D1 and D2 bands, which are related to small tetrahedral membered rings vibrations in glass, are not correlated to the macroscopic density. Consequently, they are not a reliable signature of densification phenomenon in binary glasses. Supplementary studies about the silicon coordination in the network are needed to conclude on structural origin of the silica anomaly.

The Malay and Penya Basins, offshore Peninsular Malaysia, were formed during the early Oligocene as a result of regional dextral shear deformation caused by the indentation of India into Eurasia in the early Tertiary. Pre-existing basement inhomogeneities exerted a strong control on basin development. The Penyu Basin developed, initially, as isolated grabens and half-grabens at basement fault intersections, in response to roughly N-S extension. The major structures which include low-angle listric normal faults, pull-apart rhomb grabens and flower structures, suggest that "thin-skinned" crustal extension and strike-slip tectonics have played an important role in basin evolution. Basement faults in the Malay Basin are oblique (E-W trending) to the basin trend (NW-trending). The Basin developed by transtension of NW-trending sinistral shear zone, in which fault-bounded blocks rotate in response to the shear deformation, producing a series of E-trending half-graben depocentres. The Basins were subjected to transpressive inversion during the middle-late Miocene, as a result of rotation of the regional stress field, caused by progressive indentation of India into Eurasia. Subsidence analysis suggests that lithospheric stretching was the dominant process of basin formation. The high heat flows (85-100 mW m⁻²) are consistent with stretching factors, β, of 1.2 to 4.3. In the Malay Basin, uplift of the basin flanks preceeded subsidence during the rifting phase as a result of non-uniform stretching and lateral heat flow from the centre of the Basin. Both basins are undercompensated isostatically and characterised by low negative free-air gravity anomaly in the order of -20 mGal. Undercompensation suggests that the basins were formed, partly, by "thin-skinned" crustal extension which did not involve stretching of the subcrustal lithosphere.

Abstract The Late Devonian-Early Carboniferous Drummond Basin of central Queensland, Australia is one of the oldest units of the New England Fold Belt. Samples of authigenic clay minerals have been collected from across the Drummond Basin and analysed using mineralogic, isotopic and geochronologic techniques. X-Ray diffraction analysis on 36 samples selected from six exploration wells was carried out on volcaniclastic and argillaceous sandstones and mudstones of the Drummond Basin sequence in order to ascertain authigenic illite content. Sixteen samples were found to be suitable for K-Ar dating purposes, containing abundant illite and illite/smectite mixed layers (I/S). K-Ar age dating was carried out on these selected samples yielding three age groups at 300, 250 and 200 Ma. Temperature of formation was estimated for the authigenic illite and illite/smectite minerals, based on illite crystallinity and illite content of illite/smectite mixed layers. Two groups of temperatures have been delineated, with a high temperature assemblage of between 275¨¬C-320¨¬C and a low temperature assemblage of approximately 100¨¬C. When compared with the age groups, it is seen that the older event was typically hotter. Stable isotope compositions for the authigenic clay minerals were analysed with ¥äD and ¥ä18O values of between -68¢¶ to -117¢¶ and +7.5¢¶ to +14.4¢¶ (SMOW) respectively. Isotopic compositions for the fluid in equilibrium with the clay minerals were calculated using palaeotemperatures estimated from the clay mineralogy and range between -90¢¶ and -41¢¶ and -0.6¢¶ and +8.7¢¶ (SMOW) for hydrogen and oxygen respectively. These compositions are more depleted in deuterium and more enriched in 18O than those previously reported for basins in the region. The data also produced three groups of fluid compositions, which correlate with the age distributions delineated by the K-Ar geochronology. The first fluid composition, which correlated with the Permo-Carboniferous age (~300 Ma) is interpreted to result from a mixing of Permo-Carboniferous meteoric water with highly evolved formation water trapped within the Drummond Basin since deposition of the basin. The regional extensional event at the Permo-Carboniferous boundary, which initiated the opening of the Bowen Basin to the east of the Drummond Basin allowed meteoric water to percolate deep into the basin, enabling the growth of illite rich clay minerals at this time. The second fluid group is considered to represent the evolution of Late Triassic meteoric water migrating through the Drummond Basin during another extensional period in the region at approximately 200 Ma. This event precipitated a new period of clay mineral growth in the basin (reflected in the K-Ar dates), raised the geothermal gradient in the region and extended the crust, forming new sedimentary basins within the New England Fold Belt. The third assemblage of fluid compositions were found to be very similar to the Late Triassic group, with ¥äD and ¥ä18O values plotting very close to the Late Triassic meteoric water evolution trend. This is interpreted as representing the same fluid as that which produced the Late Triassic compositions and therefore the 250 Ma ages may represent partial resetting of older ages by the Late Triassic thermal episode. However, if it is assumed that these K-Ar ages are not old ages partially reset by a thermal event, the stable isotope data could represent a mixing of Mid-Late Permian meteoric water with formation water trapped in the basin. This event may represent the regional compressive Hunter-Bowen event and may be responsible for dewatering the basin before the Late Triassic extensional episode.

The aim of this work is to study the effect of thermal history to structure and properties not only of oriented polypropylene monofilaments with different orientation but of course of isotropic non-oriented polypropylene. Term thermal history includes thermal regimes from alpha relaxation temperature (T?) to melting temperature (Tm). This work consists of three parts. The changes of dynamic mechanical properties, strength, deformation and tensile modulus of polypropylene samples according to annealing temperature (Ta) are described in the first part of this work. In the second part, the changes of crystal phase are observed. Preferentially, calorimetric behaviour (DSC), changes of crystal dimensions and orientation function of crystal phase (X-ray) are observed. Measured values from the first and the second part of this work were used for calculation of total orientation function of PP samples. Rheological measurements are shown in the third part of this thesis. Rheological measurements consist of short isothermal creep, shrinkage of free tapes and static deformation at higher temperatures. Measured rheological values were performed using rheological models. Using these models characteristics of entropic spring, instantaneous elasticity and viscosity and tendency to get to state of ease were calculated.

No description available.